In recent years, a hybrid vehicle provided with an engine including an exhaust gas type forced induction device that uses the energy of exhaust gas to pressurize the intake air has been developed. When the hybrid vehicle is travelling, the engine may be requested to stop even when the boost pressure produced by the forced induction device is high. In such a case, immediately after the supply of fuel to the engine is stopped in accordance with the request, the turbine wheel of the forced induction device continues to rotate for a while in the exhaust passage of the engine due to inertia. In such a case, gas having a high oxygen concentration is continuously supplied to a catalyst, which is located in the exhaust passage. This may increase the oxygen adsorption amount of the catalyst and lower the purification capacity of the catalyst.
Patent document 1 discloses a method for limiting decreases in the purification capacity of the catalyst. In this method, when stopping an engine as requested, the boost pressure produced by the forced induction device is lowered to decrease the rotation speed of the turbine wheel before stopping the supply of fuel to the engine. Accordingly, the rotation speed of the turbine wheel rotated by inertia immediately after the engine is stopped becomes low, and the amount of high oxygen concentration gas supplied to the catalyst is reduced. This limits decreases in the purification capacity of the catalyst.
In a hybrid vehicle provided with an engine including an exhaust gas type forced induction device, components of the forced induction device and the peripheral components of the forced induction device may become overheated if the engine is stopped while the vehicle is travelling. To avoid stopping of the engine when the forced induction device is overheated, operation of the engine is continued for a predetermined period from when the engine is requested to stop before stopping the supply of fuel to the engine. This stops the rotation of the engine crankshaft when the forced induction device is no longer overheated.